A bacon, lettuce, and tomato (BLT) sandwich is a type of sandwich which is particularly popular in the United States. As the name would imply, the sandwich classically includes bacon, lettuce, and tomato, usually with a small smearing of mayonnaise on the bread, which is typically toasted. A popular variant is the BLTA, which includes avocado in addition to the cardinal three ingredients. Some cooks have also been known to add a cooked egg to create a BELT.
Several things are at work in the marriage on ingredients included in a BLT, and some cooks get extremely serious about it. Both bacon and tomatoes have high levels of umami, the fifth taste. Studies have suggested that umami amplifies other flavors, and that combining foods high in umami will make a dish much more flavorful. Humans have clearly been aware of this fact for a long time, as many traditional dishes include several foods with high levels of umami. The lettuce provides green roughage, which contrasts with the otherwise very heavy bacon.
The bread is also an important consideration in a BLT. Rye and sourdough are two popular bread choices, although technically any type of bread can be used. Typically, the bread is toasted before the sandwich is assembled, so that it will not get soggy from the tomato and bacon grease. Toasting also adds an additional layer of crunchy texture to the sandwich. When combined together, the three principal ingredients and the bread create a simple sandwich which is also widely viewed as rather tasty.
The first recorded instance of the sandwich appears to be in an American cookbook from the late 1920s. The original cookbook called it a “bacon sandwich,” which might be confusing to people who are familiar with the British bacon sandwich, made from thick bread, bacon, and butter. A sauce such as ketchup is also commonly included in this bacon sandwich; since ketchup is made from tomatoes, it is also high in umami.
To make a BLT, the cook first needs to prepare the bacon. The bacon can be fried until tender, or made more crispy, depending on personal taste. It is usually drained or patted with a towel so that it is less oily. The bacon is added to the toasted bread, typically on top of a bed of lettuce and sliced tomato. Some cooks like to add salt and pepper to the sandwich, along with mayonnaise, while others prefer to keep the BLT simple. In either case, the BLT is best eaten hot, before the bacon starts to taste greasy.